User Authentication on ISA 2006

Hi

I’m installing ISA 2006 for the first time and are having problems with the webproxy part.

My problem is that i have created at rule that allows authenticated users to browse on protocol http and https. The users are validated in a Actice Directory. My problem is that when these users tries to stream radio on the internet they er prompted for their AD credentials, as usernames and password.
If i change the condition to be all users, they are not promted for these credentials.
What I’m trying to archive is that as they log on to a certain PC with their credentials the authentication is done in AD. There should not be any other authentication after this.

Anyone have any idea how to work around this???